In a thin-film solar cell, for example, a CIS-based solar cell, Cu(InGa)Se2, which is a chalcopyrite-type compound semiconductor comprising Cu, In, Ga, and Se, is formed as a photoelectric conversion film on a glass sheet.
In order to coat the top of a glass sheet with Cu, In, Ga, and Se and convert them into a chalcopyrite-type compound by using a multi-source deposition method, a selenization method, or the like, a heat treatment step at about 500 to 600° C. is required.
In a CdTe-based solar cell as well, a photoelectric conversion film comprising Cd and Te is formed on a glass substrate. In this case, a heat treatment step at about 500° C. to 600° C. is also required.
Soda-lime glass has been conventionally used as a glass substrate in a CIS-based solar cell, a CdTe-based solar cell, or the like. However, soda-lime glass is liable to have thermal deformation and thermal shrinkage in a heat treatment step at high temperature. In order to solve the problem, the use of high strain point glass has been currently studied (see Patent Literature 1).
In the meantime, a PDP is manufactured as described below. First, a transparent electrode such as an ITO film or an NESA film is formed on a surface of a front glass sheet, a dielectric layer is formed thereon, an electrode made of, for example, Al, Ag, or Ni is formed on a surface of a back glass sheet, a dielectric layer is formed thereon, and in addition, a dividing wall is formed thereon. Next, the front glass sheet and the back glass sheet are opposed to each other to position the electrodes and the like, and then the outer peripheral edge portions of the front glass sheet and back glass sheet are subjected to frit sealing in the temperature region of 450 to 550° C. After that, the air inside the resultant panel is evacuated to create a vacuum through an exhaust pipe and a noble gas is introduced into the panel, followed by sealing.
In the past, a glass sheet into which soda-lime glass (having a thermal expansion coefficient of about 84×10−7/° C.) was formed so as to have a thickness of 1.5 to 3.0 mm by a float method or the like was used in a PDP. However, soda-lime glass has a strain point of about 500° C., and hence is liable to have thermal deformation and thermal shrinkage in a heat treatment step. Thus, a glass sheet having the same thermal expansion coefficient as that of soda-lime glass and having a higher strain point has been currently used (see Patent Literature 2).